1. Field of the Invention
The present invention relates to a trap apparatus for use in an evacuating system for evacuating a vacuum chamber in a semiconductor fabrication apparatus or the like, and more particularly to a continuous processing trap apparatus having trap units disposed to switch between an exhaust path and a regeneration path.
2. Description of the Related Art
One conventional evacuating system will be described below with reference to FIG. 14 of the accompanying drawings. In FIG. 14, a vacuum chamber 121 serves as a process chamber for use in a semiconductor fabrication process that is carried out by an etching apparatus, a chemical vapor deposition apparatus (CVD), or the like. The vacuum chamber 121 is connected to a vacuum pump 123 by a pipe 122. The vacuum pump 123 serves to increase the pressure of a process exhaust gas from the vacuum chamber 121 to the atmospheric pressure. The vacuum pump 123 has heretofore been composed of an oil rotary pump, but mainly comprises a dry pump at present.
If the level of vacuum required by the vacuum chamber 121 is higher than the level of vacuum that can be achieved by the vacuum pump 121, then an ultrahigh vacuum pump such as a turbo-molecular pump or the like is disposed upstream of the vacuum pump 123. An exhaust gas processing apparatus 124 is disposed downstream of the vacuum pump 123, and gas components that cannot be directly discharged into the atmosphere because of their toxicity and explosibility depending on the process are treated by a process such as adsorption, decomposition, absorption by the exhaust gas processing apparatus 124, from which only harmless gases are discharged into the atmosphere. Necessary values are provided at appropriate positions of the pipe 122.
The conventional evacuating system is disadvantageous in that if a substance having a high sublimation temperature is contained in the reaction by-products contained in the exhaust gas, then the gas is solidified while its pressure is being increased, and deposited in the vacuum pump, thus tending to cause a failure of the vacuum pump.
For example, if BCl3 or Cl2 which is a typical process gas for aluminum etching is used, then the remainder of the process gas of BCl3 or Cl2 and a reaction by-product of AlCl3 are discharged from the process chamber by the vacuum pump. AlCl3 is not deposited in the suction side of the vacuum pump because its partial pressure is low. However, while AlCl3 is being discharged under pressure, its partial pressure rises, and it is deposited, solidified, and attached to the inner pump wall, resulting in a failure of the vacuum pump. The same problem occurs with reaction by-products of (NH4)2SiF6 and NH4Cl that are produced from a CVD apparatus for depositing films of SiN.
It has heretofore been attempted to heat the vacuum pump in its entirety to pass the reaction by-products in a gaseous state through the vacuum pump so that no solid substance is deposited in the vacuum pump. This attempt has been effective to prevent a solid substance from being deposited in the vacuum pump, but has been problematic in that a solid substance is deposited in the exhaust gas processing apparatus disposed downstream of the vacuum pump, thereby clogging a filled layer in the exhaust gas processing apparatus.
One solution is to install a trap apparatus upstream or downstream of the vacuum pump for trapping products for removal of components which will generate solid substances for thereby protecting various devices provided at the discharge path. The conventional trap apparatuses generally have such a poor trapping efficiency that about 60% of the components of the exhaust gas flows through the trap apparatus without being deposited in the trap unit. Those components flowing through the trap apparatus are deposited in downstream pipes and various devices. The reasons for the poor trapping efficiency are considered to be the fact that the exhaust gas flows in regions where the trapping efficiency is poor between an inner wall surface of the casing and the trap unit in the trap apparatus, and is unprocessed and discharged therefrom.